Heat the oil in a large nonstick skillet over medium heat. Add bell pepper and garlic; sauté for 2 minutes. Stir in oregano and broth. Bring to a boil; reduce heat, and simmer for 10 minutes. Remove bell pepper mixture from pan. Add beef to pan, and cook for 45 seconds. Divide beef evenly among the bottom halves of rolls; top each roll half with 1/4 cup bell pepper mixture, and 2 tablespoons giardiniera; cover with roll tops.